Competitive ability of neotropical Drosophila predicted from larval development times

Interspecific competition is a major aspect of the ecology of insect commun ities exploiting ephemeral and fragmented resources. To generate testable p redictions on the role of competition in such communities, information is r equired about the competitive abilities of the species involved. In this st udy we test whether larval development time, an important life-history trai t, can be used to predict interspecific competitive ability in neotropical Drosophila species. Based on earlier work, we predicted a negative relation ship between larval development time and competitive ability. Pairwise comp etition experiments were conducted with seven Drosophila species (in all po ssible combinations) that are known to coexist in central Panama and repres ent a wide range of larval development times. We used a novel approach to d etermine experimental densities, standardising total larval food requiremen ts, and thereby increasing the resolution for detecting general traits invo lved in exploitation competition. The effects of competition were measured by comparing values for three fitness-related parameters (thorax length, la rval survival, and total mass of emerged adults) against their values at tw o levels of intraspecific competition. The outcomes of the pairwise competi tion were significantly explained by the differences in larval development times: within species pairs, species with a longer development suffered mor e from interspecific competition than those with shorter development. It is argued that larval development time is a major determinant of competitive rank order among drosophilid species, allowing testable community-wide pred ictions. In addition, this relationship provides a basis for studying the r ole of life-history trade-offs in community-level processes. Given the gene rality of the Drosophila biology, development time is expected to play a si milar role in other insect communities exploiting ephemeral and fragmented resources.